Concrete Mix Calculator — Cement, Sand & Aggregate Quantities

This calculator works by the standard UK absolute-volume (dry-volume) method. Your required concrete volume is multiplied by the dry-volume factor of 1.54 — because 1 m³ of compacted concrete needs about 1.54 m³ of dry loose materials once voids and water uptake are allowed for — then split by the mix ratio and converted to mass using bulk densities of cement 1440 kg/m³, sharp sand 1600 kg/m³ and 20mm aggregate 1680 kg/m³.

Mix ratios explained (per m³)

• General purpose (1:2:3): 1 part cement, 2 parts sharp sand, 3 parts coarse aggregate. ≈370 kg cement (~15 × 25kg bags), 0.82 t sand, 1.29 t aggregate.
• Strong mix (1:1.5:2.5): Higher cement content for structural work. ≈444 kg cement (~18 bags), 0.74 t sand, 1.29 t aggregate.
• Weak mix (1:3:6): Lower cement for blinding and non-structural fill. ≈222 kg cement (~9 bags), 0.74 t sand, 1.55 t aggregate.
• Paving/post mix (1:2:4): Good all-rounder for fence posts and paving. ≈317 kg cement (~13 bags), 0.70 t sand, 1.48 t aggregate.

Each mix totals roughly 2.5 t of dry material per m³, in line with the ≈2.4 t/m³ density of normal-weight concrete. Figures are nominal estimates — actual yield varies with sand and aggregate moisture, grading and bulk density, so order a small margin over.

Standards reference

The 1:x:y figures above are common UK site / nominal mixes specified by volume — a builders’ merchant convention, not formal BS 8500 prescribed mixes. BS 8500 (the complementary British Standard to BS EN 206) instead specifies concrete by strength class and minimum cement content as designated mixes (GEN, FND, RC, PAV) or standardised prescribed mixes (ST1–ST5). For structural work subject to Building Regulations, specify the concrete to BS 8500 by strength class as directed by your structural engineer or Building Control rather than relying on a by-volume ratio.